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        <h2 id="什么是触发器"><a href="#什么是触发器" class="headerlink" title="什么是触发器"></a>什么是触发器</h2><p>触发器是一个特殊的存储过程，是一个与表相关联的，存储的PL/SQL程序，每当一个特定的数据操作语句（insert，update，delete）在指定的表上发出时，Oracle自动地执行触发器中定义的语句序列。</p>
<h2 id="触发器的语法"><a href="#触发器的语法" class="headerlink" title="触发器的语法"></a>触发器的语法</h2><h4 id="如何创建触发器"><a href="#如何创建触发器" class="headerlink" title="如何创建触发器"></a>如何创建触发器</h4><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line">--Print ’insert success‘ after insert record into the table.</span><br><span class="line">create [or replace] trigger trigger_name </span><br><span class="line">&#123;after|before&#125; &#123;insert|delete|update|of row_name&#125;</span><br><span class="line">on table_name</span><br><span class="line">[for each row [when(条件)]]</span><br><span class="line">declare</span><br><span class="line">begin</span><br><span class="line">    dbms_output.put_line(&apos;insert success!&apos;);</span><br><span class="line">end;</span><br></pre></td></tr></table></figure>
<h2 id="触发器的类型"><a href="#触发器的类型" class="headerlink" title="触发器的类型"></a>触发器的类型</h2><h4 id="语句级触发器和行级触发器"><a href="#语句级触发器和行级触发器" class="headerlink" title="语句级触发器和行级触发器"></a>语句级触发器和行级触发器</h4><p>语句级没有for each row，行级反之。<br>语句级触发器：在指定的操作语句操作之前或之后执行一次，不管这条语句影响了多少行。<br>行级触发器：触发语句作用的每条记录都被触发。在其中使用:old和:new伪记录变量，识别值的状态。<br><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line">insert into emp10 select * from emp where depno=10;</span><br><span class="line">-- 3 rows of records</span><br><span class="line">-- 语句级触发器：针对的是表，只执行一次。</span><br><span class="line">-- 行级触发器：针对的是行，执行了3次。</span><br></pre></td></tr></table></figure></p>
<h2 id="触发器的具体应用场景"><a href="#触发器的具体应用场景" class="headerlink" title="触发器的具体应用场景"></a>触发器的具体应用场景</h2><h4 id="复杂的安全性检查"><a href="#复杂的安全性检查" class="headerlink" title="复杂的安全性检查"></a>复杂的安全性检查</h4><blockquote>
<p>禁止在非工作时间插入新员工<br><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br></pre></td><td class="code"><pre><span class="line">--周末:to_char(sysdate, &apos;day&apos;) in (&apos;星期六&apos;, &apos;星期日&apos;)</span><br><span class="line">--上班前，下班后:to_number(to_char(sysdate, &apos;hh24&apos;)) not between 9 and 18</span><br><span class="line"></span><br><span class="line">create or replace trigger security_emp</span><br><span class="line">before insert</span><br><span class="line">on emp</span><br><span class="line">-- declare 程序中不使用变量的话，这块可以不写</span><br><span class="line">begin</span><br><span class="line">    if to_char(sysdate, &apos;day&apos;) in (&apos;星期六&apos;, &apos;星期日&apos;) or </span><br><span class="line">        to_number(to_char(sysdate, &apos;hh24&apos;)) not between 9 and 18 then</span><br><span class="line">        --禁止insert</span><br><span class="line">        raise_application_error(-20001, &apos;禁止在非工作时间插入新员工&apos;);</span><br><span class="line">    end if;</span><br><span class="line">end;</span><br></pre></td></tr></table></figure></p>
</blockquote>
<h4 id="数据确认"><a href="#数据确认" class="headerlink" title="数据确认"></a>数据确认</h4><blockquote>
<p>涨工资不能越涨越少<br><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line">--:old和:new 代表同一条记录，前者代表操作之前的值，后者反之。</span><br><span class="line">create or replace trigger check_salary</span><br><span class="line">before update</span><br><span class="line">on emp</span><br><span class="line">for each row</span><br><span class="line">begin</span><br><span class="line">    if :new.salary &lt; :old.salary then</span><br><span class="line">        raise_application_error(-20002, &apos;涨薪水不带这么玩的,涨前&apos;||:old.salary||&apos;涨后&apos;||:new.salary);    </span><br><span class="line">    end if;</span><br><span class="line">end;</span><br></pre></td></tr></table></figure></p>
</blockquote>
<h4 id="实现审计功能"><a href="#实现审计功能" class="headerlink" title="实现审计功能"></a>实现审计功能</h4><blockquote>
<p>给员工涨工资，当涨后的薪水超过6000块的时候，审计该员工的信息</p>
</blockquote>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br></pre></td><td class="code"><pre><span class="line">--创建表，用于保存审计信息</span><br><span class="line">create table audit_emp</span><br><span class="line">(</span><br><span class="line">infomation varchar2(200);</span><br><span class="line">);</span><br><span class="line"></span><br><span class="line">create or replace trigger do_audit_emp_salary</span><br><span class="line">after update</span><br><span class="line">on emp</span><br><span class="line">for each row</span><br><span class="line">begin</span><br><span class="line">    if :new.salary &gt; 6000 then</span><br><span class="line">        insert into audit_emp values(&apos;员工信息:&apos;||:new.somerows);</span><br><span class="line">    end if;</span><br><span class="line">end;</span><br></pre></td></tr></table></figure>
<h3 id="完成数据的备份和同步"><a href="#完成数据的备份和同步" class="headerlink" title="完成数据的备份和同步"></a>完成数据的备份和同步</h3><p>给员工涨薪水之后，自动备份新工资到备份表<br><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line">create or replace trigger sync_salary</span><br><span class="line">after update</span><br><span class="line">on emp</span><br><span class="line">for earch row</span><br><span class="line">begin</span><br><span class="line">    update emp_bak set sal=:new.sal where empno=:new.empno;</span><br><span class="line">end;</span><br></pre></td></tr></table></figure></p>

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